Position sensors have been used in many applications where it is desired to obtain information concerning the position of one object relative to another object or to some absolute reference such as the ground. One example of use of a position sensor is for leveling of a vehicle using air springs. The air springs are disposed between the wheel's axle or axle support (the unsprung mass) and the chassis (the sprung mass). When deflated, the chassis is lowered to rest upon the axle or support, the chassis being supported by, for example, rubber stops or the like. When inflated, the chassis is raised relative to the axle or support by the springs to the desired height. Shock absorbers are also typically provided between the chassis and the wheel axles or supports to dampen relative motion between the chassis and axles.
To raise the chassis, the air spring or springs are inflated, usually manually or, recently, by suitable controls. The pressure of the compressed air within the spring rises resulting in a corresponding lifting of the chassis by the air springs.
When the vehicle cargo changes or shifts, an indication of a non-level condition must be obtained. For manual systems a visual examination of the chassis' position is used. For automatic leveling systems, position transducers or proximity-type sensors are commonly used. These sensors provide an indication typically of a level condition, a low condition and a high condition by generating signals particular to each of the aforesaid conditions. The sensors may also be constructed to provide signals of a low-low and a high-high condition.
A drawback of the position sensors according to the prior art is that they are relatively expensive and complicated and are subject to wear and failure. Further, the sensors are in most instances disposed at the underside of the vehicle and are therefore exposed to dirt, grime, water and ice which also lead to failure of the sensors.